This invention relates to aqueous resin dispersions in which the resin produced by emulsion polymerization can for crosslinks together with the emulsifier used, to a method of producing the same and to an application thereof.
Hithertofore, aqueous dispersions of vinyl polymers, such as acrylic, vinyl acetate, styrene-butadiene and like polymers, have been widely used in various industrial fields as coating compositions or binders, for instance. These dispersions are advantageous in that since they are aqueous, the toxicity and fire hazards due to organic solvents are little with said dispersions. Accordingly, the sphere of their application is expanding more and more. On the other hand, with the expansion of their fields of use, they are more and more required to have diversified and higher-level performance characteristics. The prior art aqueous dispersions cannot fully meet such current requirements any longer and therefore their range of application is limited.
To cope with these circumstances, studies are under way to improve the performance characteristics of emulsions. Various means have been proposed for improving the performance characteristics of emulsions. As one of them, there may be mentioned the method which comprises converting films obtained from an emulsion to three-dimensional crosslinked ones. For instance, Shikaze has proposed [Japanese Kokai Tokkyo Koho (Published Unexamined Patent Application) No. 52-72731] a coating composition crosslinkable at low temperatures which contains, as a coat film-forming component, a copolymer produced by emulsion copolymerizing
(A) at least one water-soluble monomer having one or more carboxyl groups, PA0 (B) at least one oil-soluble monomer having two or more vinyl or allyl groups, PA0 (C) N-methylolacrylamide and PA0 (D) at least one monomer copolymerizable with these monomers.
This composition indeed forms a crosslinked coat film and has good solvent resistance but is unsatisfactory in water resistance because of the use, as the emulsifier for emulsion polymerization, of a low-molecular-weight emulsifier which is in general use. Another disadvantage is that toxic formalin is generated on the occasion of crosslinking.
In Japanese Kokai Tokkyo Koho No. 62-25163, an aqueous copolymer dispersion composition is proposed, which is prepared by adding a macromolecular hydrazine derivative which has at least two carbazoyl groups per molecule and is sparingly soluble in water to an aqueous dispersion of an aldehyde or ketone group-containing copolymer.
This composition can be crosslinked at low temperatures and gives partly improved performance characteristics. However, the emulsifier for emulsion polymerization as used there is a general-purpose low-molecular-weight and therefore said composition still has the problem of foaming due to the emulsifier as well as the drawback of unsatisfactory water resistance.
Japanese Kokai Tokkyo Koho No. 60-37801 proposes a method of improving the emulsion performance, namely:
A method of producing an aqueous vinyl resin dispersion for coating purposes which comprises polymerizing an ethylenically unsaturated monomer in an aqueous medium in the presence of a vinyl copolymer containing, within its molecule, 5%-40% by weight of a unit of the formula ##STR1## wherein R.sub.1, R.sub.2 and R.sub.3 each independently is hydrogen or alkyl and n is 2 to 20, and having an acid value of 30-200 mg KOH/g, said vinyl copolymer being in the neutralized state.
Japanese Patent Publication No. 60-42249 proposes the following:
A method of producing an aqueous polymer dispersion which comprises radical copolymerizing 0.1%-10% by weight of one or more .alpha.,.beta.-ethylenically unsaturated monomers having a sulfo substituent and 90%-99.9% by weight of one or more other .alpha.,.beta.-ethylenically unsaturated monomer in an aqueous medium in the presence of a water-soluble or alkali-soluble oligomer derived from an .alpha.,.beta.-ethylenically unsaturated monomer and having a terminal alkylthio group and a molecular weight of 200-5,000.
Furthermore, Japanese Kokai Tokkyo Koho No. 61-111136, Japanese Kokai Tokkyo Koho No. 61-130376, Japanese Kokai Tokkyo Koho No. 61-7368, Japanese Kokai Tokkyo Koho No. 61-136560 and Japanese Kokai Tokkyo Koho No. 61-133137 propose the following:
A method of producing an emulsion which comprises emulsion copolymerizing a monomer or monomers using as the emulsifier an oligomer or oligomers of the general formula (1) and/or (2) ##STR2## wherein R.sub.1 is straight-chain primary alkyl or branched primary or secondary alkyl containing 6-16 carbon atoms, or a mixture of these, R.sub.2 to R.sub.5 each independently is hydrogen, carboxyl, carboxymethyl or alkyl of 1 to 5 carbon atoms, or ammonium base, amine base, alkali metal base or alkaline earth metal base thereof, R.sub.6 is hydrogen, halogen or alkyl, X is cyano or --COOCH.sub.3, Y is hydrogen, ammonium, amine base, alkali metal or alkaline earth metal, and a and b each independently is a number of 1-100; as well as an adhesive composition, an adhesive for carpet lining, and an adhesive to be applied to fibrous base materials, each containing said emulsion.
As compared with the use of a low-molecular-weight emulsifier such as sodium dodecylbenzenesulfonate or nonylphenol-ethylene oxide adduct, the use of the above-mentioned polymer emulsifier or oligomer emulsifier is advantageous, for example, in that foaming is slight and that the water resistance can be improved. However, these techniques allow the hydrophilic polymer used as the emulsifier to remain in films after film formation without reacting in any way. Accordingly, such performance characteristics as water resistance are still impaired although the extent of impairment is less as compared with those low-molecular-weight emulsifiers which are in general use.
As mentioned above, the known techniques or methods each still has a drawback or drawbacks or fails to afford satisfactory performance characteristics.